A network packet is a formatted data item that is transmitted by a network. The network that transmits network packets is a packet transport network. Formatting data into packets allows for packet switching and sharing of network bandwidth among a large number of users. A packet includes control information and user data, which is also known as the payload. Control information includes metadata for delivering the payload, such as source and destination network addresses, error detection codes, etc. Typically, control information is found in packet headers and/or trailers.
Time-division multiplexing (TDM) is a method of transmitting and receiving independent signals over a common signal path. TDM may be performed by synchronized switches at each end of the transmission line so that each signal appears on the line only a fraction of time in an alternating pattern. In circuit-switched networks, such as the public switched telephone network (PSTN), multiple subscriber calls over the same transmission medium may be transmitted to effectively utilize the bandwidth of the medium. TDM allows transmitting and receiving telephone switches to create channels within a transmission stream. For example, a standard DS0 voice signal has a data bit rate of 64 kbit/s. A TDM circuit runs at a much higher signal bandwidth, permitting the bandwidth to be divided into time frames (time slots) for each voice signal which is multiplexed onto the line by the transmitter. Each voice time slot in the TDM frame is referred to as a channel. For example, E1 contain 30 digital voice channels, while T1 contain 24 channels. Additional examples of TDM telecommunication system include SONET/SDH, ISDN, etc.